When ready-to-eat factory-prepared dishes are to be heated in microwave ovens, the package contents will as a rule be unevenly heated. One manner of remedying this drawback is to arrange a material of a special kind in the package in those portions of the package contents that normally are heated to a lesser degree than other portions. This special material is chosen for its capacity to improve absorption of the microwaves and consequently the package contents located in the area where the special material is present are heated indirectly via the high-absorption material. One alternative is to use materials that rather than absorbing microwaves actually prevent such waves from reaching their target. This kind of material therefore is positioned in the area of the package that normally receives most heat. Packages fitted with integrated special materials obviously are more expensive to produce while at the same time they add to the complexity of the manufacturing process.
Furthermore, the keeping qualities of ready-to-eat food kept under refrigeration are limited in the case of traditionally packaged heat-and-eat dishes. The prepared food is transferred to packages, which are then subjected to a vacuum pressure, alternatively are filled with an inert gas, such as carbon dioxide. Vacuum-packing often is not sufficient to ensure the keeping qualities of the ready-cooked food inside the package over longer periods. The transfer of the ready-cooked food onto the package also puts the food into contact with the surrounding air, which further shortens the period of freshness of the food.